You cannot braze a vacuum component with flux. Whatever the flux leaves behind will outgas into the chamber for the rest of its life. Vacuum brazing removes that problem by doing the whole operation in a vacuum furnace, where the oxide layer on the filler metal breaks down thermally rather than chemically.
Why vacuum brazing and not torch or furnace brazing with flux
Flux works by chemically dissolving oxides, and the residue stays on the part. In atmospheric furnace brazing that residue is normally acceptable; in a vacuum system it is a contaminant source. Vacuum brazing relies on the low oxygen partial pressure inside the furnace to dissociate the oxide film on the filler metal, so no flux is required and the joint comes out clean.
What vacuum brazing is good for
It suits assemblies that must be leak-tight and cannot be welded — thin-to-thick transitions, dissimilar thickness joints, internal joints that a torch cannot reach, and multi-point joints that would distort if welded sequentially. It also produces a continuous fillet rather than a local spot of heat, so distortion is lower than with welding.
Typical joint quality we work to
Full fillet formation with no voids or incomplete penetration, braze alloy selected for the service temperature so the joint does not remelt during a subsequent bake-out, and a leak-tight result verified by helium mass-spectrometer testing rather than by visual inspection.
Interaction with bake-out
This is the point most often missed. If the chamber will be baked at 250 °C, the braze filler must have a melting point comfortably above that, or the joint will soften. We select the filler against the customer's bake-out temperature, not just against room-temperature strength.
What we control in-house
- 304 / 316L stainless steel and 6061 / 5083 aluminium fabrication
- Clean-environment TIG welding with full penetration and no micro-porosity
- Helium mass-spectrometer leak testing to 1 × 10⁻⁹ mbar·l/s
- In-house electropolishing and passivation — not subcontracted
- Chamber bake-out to 150–400 °C for UHV outgassing control
- Precision-machined ISO-KF, ISO-K and CF (ConFlat) flanges
- Zeiss CMM verification to ±0.02 mm across large work envelopes
- 12 m gantry CNC machining — 12 m × 4 m × 2 m envelope
- SEMI-referenced documentation and inspection protocols
Frequently asked questions
What is the advantage of vacuum brazing over welding?
A brazed joint is continuous and made at a lower temperature than welding, so distortion is much lower and thin sections can be joined to thick ones without burn-through. It also reaches internal joints that a welding torch cannot access.
Can vacuum-brazed joints be used in UHV service?
Yes, provided the filler alloy is chosen for the bake-out temperature and the assembly is cleaned for vacuum service afterwards. Because there is no flux, there is no flux residue to outgas.
Which filler metals do you use?
The filler is selected against the base material, the service temperature and the required joint strength. For stainless assemblies the deciding constraint is almost always the bake-out temperature rather than the ambient-temperature strength.
Does vacuum brazing work for aluminium?
Aluminium requires its own vacuum brazing cycle and filler system because of the tenacious surface oxide. It is done, but it is a different process from stainless brazing and the joint design rules differ.
How do you verify a brazed joint?
By helium leak testing rather than by visual inspection. A joint can look perfectly filleted and still contain a void path through it, so the acceptance criterion is the leak rate.
Related capabilities
Need this made to spec?
Send the drawing or the specification and we will come back with a DDP price, lead time and inspection plan.